March 12, 1897.] 



SCIENCE. 



433 



systems support such a comparison. Limu- 

 liis has in each ventral ganglion two sets 

 of transverse commissures, four or five 

 bundles below the remnant of the median 

 furrow, and two above it. Thus a rudi- 

 mentary ' canali^ centralis ' is formed in the 

 adult with commissures on either side of it. 

 The entire set of neural commissures in the 

 hind-brain of Limulus probably represent 

 the beginnings of the cerebellum. In the 

 fore-brain region of Limulus are three main 

 systems of commissures, having the same 

 general relation to the brain that the su- 

 perior, middle and inferior commissures 

 have in Vertebrates. 



Life History and Sexual Relations of the Ento- 

 conchidm. IST. E. Haeeington. 

 The Entoeonehidce are a very rare degen- 

 erate type of molluscs, first observed by 

 Johannes Miiller. Since that observation, 

 in 1852, but one contribution to their mor- 

 phologj'^ has appeared. From the discovery 

 of a new genus of this family, living under 

 new conditions, the following facts may be 

 observed : 



1. Ontogenetically these forms do not pass 

 through a Thyca or Stilifer stage, as has 

 been suggested by recent hypothesis. They 

 are ejected through the cloacal wall (as 

 are the Cuvierian organs), or else are evis- 

 cerated, escaping from the sac by dehis- 

 scence. 



2. The larva is free swimming and enters 

 the new host with the water taken into the 

 respiratory system, penetrating either the 

 walls of the latter or those of the alimen- 

 tary tract. 



3. The adult sac is produced by the enor- 

 mous outgrowth of the genital organs and 

 subsequent degeneration of head parts. 



4. For the first time in these degenerate 

 shelless molluscs, separate sexes are ob- 

 served. The males carrj^ spermatophores. 

 This observation takes Entoconcha from the 

 evidence employed to show that Hermaph- 



roditism is simpler and more primitive than 

 Gonochorism in the Mollusca. 



Budding in Clavilinidce. G. Lefevee. 



The only genera of this family of com- 

 pound Ascidians whose bud development 

 has hitherto been described are Clavilina 

 and Perophora, but the following is a brief 

 account of the process as it occurs in 

 another genus, Ecteinascidia. The material 

 was obtained in Jamaica and belongs to the 

 species E. turbinata, Herdman. Although 

 in external appearance the zooids resemble 

 those of Clavalina, as they are quite elonga- 

 ted and the two siphons are at the anterior 

 end, the species shows a closer similarity to 

 Perophora, both in the structure of the adults 

 and the mode of development of the buds. 

 It difixjrs from the former and agrees with 

 the latter in the total absence of an epi- 

 cardium and abdomen, but is distinguished 

 from these two forms by the presence of 

 perfect internal longitudinal bars in the 

 wall of the branchial sac. There is nothing 

 like the displacement or rotation of the 

 inner vesicle of the bud rudiment, which has 

 been described for Perophora. 



The ectoderm of the bud is directly de- 

 rived from that of the stolon and the inner, 

 or ' endodermal,' vesicle from the stolonic 

 septum, which, however, is not a flat parti- 

 tion, but a tube enclosed within the ecto- 

 derm and bathed on all sides by the blood. 

 The bud is connected with the stolon at its 

 posterior end, and its long axis is perpen- 

 dicular to that of the stolen, as in Clavelina. 



The pericardium is usually the first organ 

 to appear, and is formed by cells which 

 wander out from the wall of the inner 

 vesicle far back on the right side. 



The dorsal tube has a similar origin, but 

 arises at the extreme anterior end of the 

 vesicle, while the ganglion is differentiated 

 out of the dorsal wall of the tube. 



The sexual organs are also formed from 

 cells which are given off from the wall of 



